/Engine/Source/Developer/ToolMenus/Public/ToolMenus.h
Delays menu registration until safe and ready Will not trigger if Slate does not end up being enabled after loading Will not trigger when running commandlet, game, dedicated server or client only
static [FDelegateHandle](API\Runtime\Core\Delegates\FDelegateHandle) RegisterStartupCallback ( const FSimpleMulticastDelegate::FDelegate & InDelegate )